A METHYLATED NEUROSPORA 5S RIBOSOMAL-RNA PSEUDOGENE CONTAINS A TRANSPOSABLE ELEMENT INACTIVATED BY REPEAT-INDUCED POINT MUTATION

In an analysis of 22 of the roughly 100 dispersed 5S rRNA genes in Neu rospora crassa, a methylated 5S rRNA pseudogene, Psi(63), was identifi ed. We characterized the Psi(63) region to better understand the contr ol and function of DNA methylation. The 120-bp 5S rRNA-like region of Psi(63) is interrupted by a 1.9-kb insertion that has characteristics of sequences that have been modified by repeat-induced point mutation (RIP). We found sequences related to this insertion in wild-type strai ns of N. crassa and other Neurospora species. Most showed evidence of RIP; but one, isolated from the N. crassa host of Psi(63), showed no e vidence of RIP. A deletion from near the center of this sequence appar ently rendered it incapable of participating in RIP with the related f ull-length copies. The Psi(63), insertion and the related sequences ha ve features of transposons and are related to the Fot1 class of fungal transposable elements. Apparently Psi(63) was generated by insertion of a previously unrecognized Neurospora transposable element into a 5S rRNA gene, followed by RIP. We name the resulting inactivated Neurosp ora transposon Punt(RIP1) and the related sequence showing no evidence of RIP, but harboring a deletion that presumably rendered it defectiv e for transposition, dPunt.